Active-matrix flat-panel imagers (AMFPIs) have undergone extensive research and development since their initial conception approximately 14 years ago. As a result of these efforts, this x-ray imaging technology is presently being introduced to a wide variety of clinical environments. While diagnostic AMFPIs offer definite benefits over older conventional devices, present indirect and direct AMFPI technologies suffer from inherent limitations that severely restrict their performance under the low-exposure conditions commonly encountered in fluoroscopy. Specifically, existing AMFPI devices suffer from a relatively large additive noise compared to the gain of the system. Research leading up to this proposal has specifically identified two innovative strategies that have shown particular promise for eliminating these limitations. Consequently, the question to be examined in the proposed research is: "Is it feasible, through the development and incorporation of specific fundamental innovations to imager design, to develop large area, advanced technology, fluoroscopic AMFPIs with performance levels matching or exceeding those of x-ray image intensifiers under all conditions, and capable of high radiographic imaging performance?" To address that question, this grant application proposes an ambitious, focused program of research to quantitatively investigate the two strategies: one involving in-pixel amplification circuits coupled to a continuous photodiode structure for indirect detection of the incident radiation; and the other involving a high-gain photoconductive converter material (mercuric iodide) for direct detection. Through the iterative development of a series of small and large area prototype imagers incorporating these innovations, the effectiveness of the strategies will be quantitatively examined over the relevant imaging conditions. The successful conclusion of this research will facilitate the creation of one of more highly advanced x-ray imaging technologies allowing the realization of higher performance AMFPI systems. Such systems would offer spatial resolution and detective quantum efficiency (DQE) performance superior to existing XRIIs and DQE performance superior to existing film-screen and computed radiography systems under all clinical conditions. The development of technologies exhibiting such performance levels could have a profound impact on digital radiology.